Plankton represent a highly diverse group of marine organisms which occupy a range of depth levels in the water column and are crucial to the marine ecosystem. Microplankton vary in size and include microorganisms as small as approximately 10 μm to 100 μm up to larger organisms such as jellyfish. These organisms generally drift through the water column of the pelagic zone of the oceans or fresh bodies of water by means of the water current or through independent movement. As a group, plankton form the basis of many marine food webs and are an important food source to other marine organisms. Plankton are also critical contributors to nutrient cycling in the ocean. Because plankton are a crucial food source for many marine organisms, the fishery industry is highly dependent upon planktonic organisms as a source of fish productivity. Additionally, plankton studies also assist scientists in understanding the different qualities of aquatic bodies including changes in fish stocks, pollution, and climate.
Previous methods of monitoring these pelagic marine organisms have generally included large-scale ocean surveys that perform collection via nets and sampling bottles in order to quantify the present states of the ocean such as species, life stages, larvae quantities, among other biological aspects. Such methods are most suited collection for robust marine organisms but typically destroy fragile structures such as gelatinous plankton and marine snow particles. Furthermore, abrupt changes to pressure, temperature, and light associated with removal of water from in situ conditions may also have undesirable consequences to the sampled organisms. Additionally, these methods tend to be quite labor-intensive and provide only a highly limited view in time of the sampled marine environment with high variation in the concentration, type, and quantity of microorganisms. The sampling nets or bottles are also unsuited to provide adequate depth information with respect to the plankton populations in the water column since the collected plankton are mixed within the sample.
Methodologies providing non-intrusive techniques (e.g., in situ sampling/measurements) are preferred as there is also substantially less experimental error introduced in the qualification and quantification analysis of the sampled marine microorganisms. In addition, the ability to perform in situ evaluation greatly enhances the experimental data, providing a more accurate perspective into the natural environment without excessive disruption. Therefore, techniques involving in situ monitoring and data collection of microorganisms is highly desirable.
Advances in imaging technology have allowed for greater spatial and temporal resolution of the plankton populations through optical sampling methods. Typical optical systems have struggled in processing the large volume of data and classifying the plankton with reliable accuracy. Moreover, existing imaging devices may disrupt the natural environment with excessive illumination, causing certain species to avoid the light (and imaging), skewing the data of the sampled population.
Beyond the challenges presented by capturing images of these microorganisms are the difficulties in identifying the plankton communities and other aquatic particles. Image identification of plankton samples must balance accuracy, or how well the system compares with traditional methods, with efficiency and repeatability in order to handle large volumes of material. Previous methods to identify and categorize various species of plankton and other microorganisms typically involved individualized analyses; computer identification has often proven to be difficult and less precise than human identification. Therefore, it is highly desirable to provide an inexpensive submersible imaging system capable of high volume and accurate classification analysis which limits the disruption to the aquatic environment.